1. Field of the Invention
The present invention relates to a heat resistant and explosion-proof type permanent magnetic synchronous motor, more particularly to a heat resistant and explosion-proof type permanent magnetic synchronous motor provided to actuate a control rod in a pressure container of nuclear reactor exposed in severe circumstances such as temperature near 330 centigrade or pressures near 100 atmospheric pressure and so on.
2. Description of the Prior Art
Conventionally, this kind of motor was installed out of the pressure container of nuclear reactor, therefore, it was not necessary to provide a motor which could endure severe circumstances such as temperature near 330 degrees centigrade or temperature near 100 times atmospheric pressure.
Furthermore, the type of motor specially made for severe circumstances by the teachings of conventional technologies was an induction motor of a canned type which would endure either high temperature and high pressure, for example as shown in Japanese Utility Model No. SHO 59-8430 or Unexamined Utility Model Application No. SHO 59-14951. In other words, there has been not known a heat resistant and explosion-proof type permanent magnetic synchronous motor capable of not only high temperature but high pressure as well.
In the case of above conventional motors, since the motors are installed out of the pressure container of nuclear reactor, they need to serve as a boundary between high pressure side of the pressure container and the low pressure side of the outside. Accordingly, if a small accident occurs in a control rod actuating apparatus driven by the motor, it is feared the pressure difference between outside and inside of the pressure container may induce a serious accident such as the control rod flying out of the pressure container. For this reason, it was required to provide a supporting structure on an upper portion of the pressure container for supporting the control rod actuating apparatus. Also, various inspectional experiments need to be done to assure operational safety under the assumption that a serious accident may occur if the control rod flies out of the pressure container.
On the other hand, if it were possible to provide the control rod actuating apparatus in the pressure container, it would not be necessary to provide a supporting structure out of the pressure container. Furthermore, a nuclear reactor can be made compact in size and light in weight, and possibility of the control rods flying out accidentally can be substantially eliminated. In improving a conventional induction motor of canned type made for special applications, the aim has to install the control rod actuating apparatus in the pressure container. In this case, the properties of induction motors make it difficult to maintain their stopping condition to hold control rods or actuate the control rods by extremely low rotational speed. This is because, in the induction motors, the secondary electric current required for a rotor to generate torque is an electric current induced by speed electromotive force. It was therefore a problem that a sufficient secondary electric current would not flow through the rotor in a stopped condition or at extremely low rotational speeds.